Allow demand energy to be None for eiger parameters

[olliesilvester]

Part of DiamondLightSource/mx-bluesky#1471

If the expected energy is None, we should use the current energy instead.

Typing should have caught this issue, but we had it disabled for the whole file - we disabled it because old ophyd-devices don't play nicely with typing. I've added individual type ignores instead so that real typing errors still get noticed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.11%. Comparing base (9435d9e) to head (d2a31fc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1737   +/-   ##
=======================================
  Coverage   99.11%   99.11%           
=======================================
  Files         281      281           
  Lines       10665    10667    +2     
=======================================
+ Hits        10571    10573    +2     
  Misses         94       94           

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[DominicOram]

Great, thanks!